[ SINGLE LINE DIAGRAM SYMBOLS · COMPARISON ]
IEC vs ANSI single line diagram symbols
The same switchboard can be drawn two ways. US one-lines use IEEE 315 symbols and ANSI device numbers; international one-lines use IEC 60617. Busbars, grounds and meters look the same, but switching devices, relays and fuses do not.
- ANSI practice
- IEEE 315 symbols and IEEE C37.2 device numbers
- IEC practice
- IEC 60617 symbols, protection written as quantity and limit
Sources and machines
All sources and machinesSymbolANSI / IEEEIEC 60617Difference
GeneratorS00819ANSI: A circle with a sine wave or the letter G, often with the rating written beside it. IEC: The general machine symbol, a circle, with G for generator and a tilde for alternating current.
MotorS00819ANSI: A circle with M, with the horsepower or kW written beside it. IEC: The machine circle with M and a tilde for an AC motor.
Transformers
All transformersSymbolANSI / IEEEIEC 60617Difference
TransformerS00841ANSI: Two coils either side of the core lines. Many US one-lines also use the two-circle form. IEC: Two overlapping circles. The coil form is S00842. Winding connections are shown with a star or delta inside each circle (S00858 is star-delta).
Three-winding transformerS00844SameDrawn the same way: three overlapping circles. The coil form is S00845.
Current transformer (CT)S00850ANSI: A small loop beside the conductor, with a polarity dot and the ratio written next to it. IEC: A circle threaded on the conductor. The coil form is S00851.
Voltage transformer (VT)S00841ANSI: A small two-coil transformer tapped off the bus, often labelled PT with its ratio. IEC: The two-circle transformer symbol, drawn small and tapped off the busbar, with its ratio beside it.
Switching devices
All switching devicesSymbolANSI / IEEEIEC 60617Difference
Circuit breakerS00287ANSI: A square in the line, often marked 52, the ANSI device number for an AC circuit breaker. IEC: A switch with a cross at the fixed contact. The cross is the circuit breaker function, S00219.
Draw-out circuit breakerS00287ANSI: The breaker square with a chevron on each side, showing the disconnecting contacts. IEC: The IEC breaker with chevrons for the plug-in contacts on each side.
Low voltage circuit breakerS00287ANSI: A curved arc between two contacts, with the frame and trip ratings written beside it. IEC: IEC uses one breaker symbol at every voltage: a switch with a cross. Trip units can be added as qualifiers.
Disconnect switchS00288ANSI: A switch blade between two contacts, sometimes marked 89, the ANSI number for a line switch. IEC: A switch with a short bar across the fixed contact. The bar is the disconnector function, S00220.
Load break switchS00290ANSI: Usually drawn as a disconnect switch and marked as load break in its label. IEC: A switch with both the disconnector bar and the switch-disconnector mark at the fixed contact.
Earthing switchS00288 + S00200ANSI: A switch blade to the ground symbol. IEC: A disconnector connected to the earth symbol.
ContactorS00284ANSI: A normally open contact, two parallel lines, marked M or with the starter size. IEC: A switch with a half circle at the fixed contact. The half circle is the contactor function, S00218.
FuseS00362ANSI: An S-shaped curve in the line. A plain rectangle is also used. IEC: A rectangle with the conductor running through it.
Fused switchS00370ANSI: A disconnect switch with a fuse in series below it. IEC: The fuse drawn on the switch blade, with the switch-disconnector marks at the fixed contact. A fuse-disconnector is S00369.
Automatic transfer switchSameUsually drawn the same way, as a labelled box, or as two interlocked switches.
Protection and metering
All protection and meteringSymbolANSI / IEEEIEC 60617Difference
Protective relayS00327ANSI: A circle with the ANSI device number of each function, for example 50/51 or 87T. See ANSI device numbers. IEC: A box with the quantity and its limit inside: I> for overcurrent, U< for undervoltage, Id> for differential.
Surge arresterS00373ANSI: An arrow pointing to a gap, connected to ground. Drawings vary, so check the legend. IEC: A rectangle with an arrow pointing down inside it, connected to earth.
Neutral grounding resistorANSI: A zig-zag resistor to ground, with its current and time rating. IEC: A rectangle, the IEC resistor, to earth.
Energy meterS00912ANSI: A circle marked WH or kWh. IEC: IEC draws counting instruments as a rectangle, with the unit inside.
Busbars and connections
All busbars and connectionsSymbolANSI / IEEEIEC 60617Difference
Crossing, not connectedANSI: Older US drawings use a small hop where one line jumps the other. On CAD drawings a plain crossing is common. IEC: A plain crossing, with no dot.
Loads and power electronics
All loads and power electronicsSymbolANSI / IEEEIEC 60617Difference
Capacitor bankS00567ANSI: One straight and one curved plate, connected to ground for a grounded wye bank. IEC: Two straight parallel plates.
ReactorS00848ANSI: A coil drawn as a row of loops. IEC: A three-quarter circle on the conductor. The loop form, like the US one, is S00849.
Variable frequency driveS00213ANSI: A box marked VFD or VSD with its rating. IEC: The converter square with a diagonal, with alternating current on both sides: a frequency converter.
RectifierS00894ANSI: A box with a diode, or marked RECT. IEC: The converter square with AC in and DC out.
Which one is on your drawing?
Look at the circuit breakers. Squares marked 52 and relay circles with numbers mean ANSI. Switch blades with a cross at the contact and relay boxes marked I> mean IEC. Many international projects mix the two, for example IEC symbols with ANSI device numbers next to the relays, so check the legend sheet.
Frequently asked questions
What is the main difference between IEC and ANSI symbols?
Switching devices. ANSI draws a medium voltage breaker as a square marked 52; IEC draws every switching device as a switch blade with a mark at the contact: a cross for a breaker, a bar for a disconnector, a half circle for a contactor.
Do IEC drawings use ANSI device numbers?
Pure IEC drawings write protection as quantity and limit, such as I>. In practice many international projects add ANSI numbers such as 50/51 because relay manufacturers and engineers know them.
Which symbols are the same in IEC and ANSI?
Busbars, connection dots, ground, batteries, meters such as ammeters and voltmeters, and three-winding transformers are drawn the same way in most legends.
Every breaker and transformer on your one-line, tested and energised.Deskely holds the tag register, test records and punch items for every electrical tag on your project, through to handover.
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The symbols on this page were drawn by Deskely and are free to use. Standards are revised and every project issues its own legend sheets, which take precedence.